Garlic has been used for medicinal purposes for at least five thousand years. The Greeks and Romans used raw garlic as an antibiotic, to cure coughs, to heal wounds and sores and to prevent colds.
In recent centuries garlic has been reputed to provide protection against bubonic plague and to cure cholera and smallpox. Garlic extract is often prescribed as an antibiotic, particularly in cases of ear, nose and throat infections, by doctors in Russia and Eastern Europe. It was also widely used during the Second World War by German and Russian doctors to treat septic wounds when drugs were scarce.
Garlic has been shown to reduce total cholesterol levels when compared to a placebo in ten studies, but studies where the diet was strictly controlled in order to ensure that changes in cholesterol could not be attributed to eating different food failed to show any significant effect of garlic on cholesterol levels.1
Recent research has shown that garlic contains a potent anti-bacterial, allicin, the compound responsible for the pungent taste and smell of garlic. Garlic also contains adenosine, a chemical which has been shown to reduce levels of cholesterol in the blood.
Chinese doctors report that a garlic oil extract given intravenously to bone marrow transplant patients was more successful than a conventional drug regimen in preventing the development of CMV-related interstitial pneumonia.2 However, this study was conducted in only a small number of patients and does not provide enough information on the standard incidence of CMV-related interstitial pneumonia amongst bone marrow patients treated in China to judge whether it is a superior form of treatment.
Garlic extract has also been used in combination with amphotericin B to treat cryptococcal meningitis in cases where amphotericin B has failed to produce improvement or had produced marked liver toxicity.3 It is also widely used as anti-fungal agent in China.4
The mechanism suggested to account for garlic's anti-bacterial, anti-viral and anti-protozoal effects is its ability to affect lipid and cholesterol synthesis in the capsule of the micro-organism. Garlic is unable to inhibit the replication of viruses which lack a lipid capsule. Its inhibitory effects have not been tested on HIV.
There is some dispute amongst garlic experts as to the best form in which to take garlic in order to benefit from its potent anti-bacterial effects.
Raw, crushed garlic is said by some to be the most potent form but taking garlic in this way is uncomfortable for many because it causes burning in the mouth and throat, and leads to an unavoidable stench as garlic fumes are excreted from the pores and on the breath. It may also cause discomfort in the gut: diarrhoea, vomiting, nausea and skin rash have been reported. Use in very large quantities for long periods could result in bleeding and ulceration. In addition, garlic can also inhibit blood clotting, and if taken in large quantities for long periods, may interfere with thyroid function.
Mixing raw garlic with honey may make it more palatable, as may chopping up the garlic and swallowing it without chewing, but most people prefer garlic to be cooked. Whether or not cooking garlic diminishes some of its beneficial effects is a matter of debate amongst garlic researchers.
Garlic pills are now widely available in health food stores, containing garlic oil. This is probably less effective than fresh garlic because it contains diallyl disulphide, a weaker anti-bacterial than allicin. However, aged raw garlic extract is thought to be as potent as raw garlic, and does not cause the bad breath, flatulence or body odour associate with raw garlic and garlic oil. Animal toxicity studies suggest it can be used at very high doses for long periods without appreciable toxicity.5
Garlic supplements have been shown to impact on the blood levels of some anti-HIV drugs. Specifically, levels of saquinavir have been reduced by half when garlic supplements are taken concurrently with saquinavir, while ritonavir levels are increased by very high garlic intake. Experts believe that low to moderate intake of cooked garlic in food does not impact on drug levels.6